Managing the uncertainty and risk of wildfires and smoke

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by Courtney Llewellyn

At the virtual Wine & Grape Symposium this year, it was noted that an unprecedented fire season coincided with an unprecedented pandemic. There were more than 100 major fire events which affected a total land area of about 10 million acres – resulting in more than $680 million in 2020 crop losses in California and Oregon alone. The long-term impact is estimated to be $3.7 billion in losses to the wine industry, lasting into 2023.

What are the next steps then? Developing metrics to accurately describes problems, understanding how the metrics relate to quality and leveraging that knowledge to drive specific outcomes. “Once we have a good hold on metrics, we can then move on to a model, then move on to management,” said Bruce Pan of E&J Gallo Winery in California.

However, the nature of smoke-related risk is complex and can be difficult to model. The volatile phenols that negatively impact grapes depend on a fire’s fuel sources, the extent and timing of smoke exposure (and even the age of the smoke), how compounds transform during uptake in the fruit, during fermentation and even during aging, and varietal-specific effects. “We’re getting better at identifying the full cast of players, but we’re still trying to figure out how to treat them,” Pan said.

How to Manage Uncertainty

There are three ways to manage uncertainty: preventative, prescriptive and remedial actions. Preventative actions include stopping the problem at the source, reducing vineyard exposure to smoke and/or blocking the accumulation of volatile compounds in grape material. This would involve utilizing fire breaks, barrier sprays, early warning systems and even grape breeding for increased resistance.

Prescriptive actions are managing and mitigating the symptoms of the problem and using winemaking practices that address the problem. Managing extraction of volatile compounds, pre-fermentation fining, yeast selection and enzymes and isolating fractions would all be prescriptive.

Remedial actions restore suitable functionality and ideally recover the original intended use of the grapes and can involve post-fermentation strategies, such as post-fermentation fining, selective removal of smoke-related compounds or masking or balancing smoke characteristics with oak barrel aging.

Anita Oberholster, Ph.D., UC-Davis, said the biggest problem with smoke taint is that it overpowers a wine and makes it one-dimensional. “For me, what’s very characteristic is an old ashtray/campfire feel at the back of your throat,” she said.

The difference between barrel toasting and a wildfire is that in barrel toasting, there’s a controlled release of volatile phenols, which gives wine a specific taste. The smoke taint phenols in the atmosphere soak into the grapes’ skin/epidermis and are absorbed very quickly. You may not be able to smell volatile compounds, but the enzymes in your saliva can release them.

So what happens next? In the short term, wider availability of testing for volatile compounds needs to be offered and the relative efficacy of management practices need to be validated. Over the longer term (the next three or more years), there need to be improved metrics to better predict sensory risk; prevention strategies to block the uptake of smoke-related compounds; improved remediation strategies; better early warning systems; and increased breeding programs to decrease susceptibility to smoke effects.

How to Mitigate Smoke Taint

There are different treatment options grape growers are currently using to lessen smoke taint problems. With white wines, gently processing the grapes helps – hand picking, light pressing, even fining with activated charcoal. Using a fruity yeast and building the body with different winemaking tools has also showed promise.

With low to medium smoke-impacted red grapes, experts suggest using fruity yeast and light toasted oak with no smoky or related aromas. You want to uplift the fruit and hide any smokiness. Rosés, unfortunately, are not always an economically viable option after smoke taint has occurred (because volatile phenols may have a lower threshold in this matrix than in red wines).

Take a fruit sample close to harvest when you have smoke exposure concerns. It helps to compare it to a previous (or baseline) sample from a year without smoke exposure. You can also do small fermentations (30 to 40 clusters, one per vine) to see what the end effects may be. The larger the sample, the more representative of your vineyards it is. Follow up with sensory evaluations of those small-scale fermentations. It turns out up to 25% of people don’t even notice smoke taint.

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